The present invention relates to an apparatus and method for vertically drilling the top brick of a coke oven proper by rotary drilling, and more particularly the invention relates to an apparatus whereby a temperature measuring hole having accurate verticality and depth is formed at each of desired positions in the top of a coke oven in operation, e.g., the brick just above the combustion chambers adjoining the carbonization chamber where the internal temperature is as high as 800.degree. to 900.degree. C. without causing damages to the surrounding and a drilling method which utilizes the apparatus.
Recently, a "coke oven combustion computer control system", which is extremely effective for the labor saving and energy saving in the operation of coke ovens and the improvement of coke properties, particularly coke strength, has been developed and put in use. The key point of this system is the temperature measurement of the combustion chambers and the computing control of the detailed oven temperature control and gas flow regulation required for maintaining the proper combustion chamber temperature distribution is effected by a computer in accordance with the measured temperatures. In this temperature measurement of the combustion chambers, if the temperature measuring thermocouples are directly exposed to the gas passages, the thermocouples will be damaged and become unusable in a period of 1 to 2 months due to the elevated temperatures and the corrosive components in the waste gases thus making it inevitable to indirectly measure the temperature through the refractory brick of the oven top from within the brick. As a result, it is necessary to form a large number of temperature measuring holes in the top of a coke oven, that is, it is necessary to make one or more holes per row of combustion chambers in the case of a large oven and 100 or more temperature measuring holes in the case of an oven battery including 100 or more combustion chambers.
In such a case, temperature measuring holes must be accurately formed in the oven top brick so as to ensure the temperature measurement and measuring accuracy as close to the actual gas temperatures as possible. While newly built ovens may be constructed by using bricks so shaped as to provide the required temperature measuring holes in the course of the production of oven top bricks, the life of the coke ovens is from 20 to 30 years and therefore the introduction of the previously mentioned combustion control system and hence the provision of a large number of temperature measuring holes are effected on the existing coke ovens in operation. In this case, the following problems must be overcome in connection with the provision of temperature measuring holes.
(1) Since the temperature of the top brick of a coke oven in operation is between 800.degree. and 900.degree. C. at the temperature measuring portion (the deep portion of the oven top wall near the combustion chamber) and the temperature is increased due to the generation of frictional heat caused by the cutting and since the refractory brick having a high degree of hardness is to be drilled, it is necessary to develop an exclusive refractory brick drilling bit which has excellent heat-resisting and wear-resisting properties. PA1 (2) The bit must be changed at any time during the drilling of the one and the same hole in accordance with the difference in temperature due to the different hole depths, the drilling purposes, the wear of the bit, etc. PA1 (3) The vertical accuracy of temperature measuring holes should preferably be 1/500 or less. In other words, if the drilled hole vertical accuracy is insufficient, the forward end of a vertically inserted thermocouple tends to contact or come excessively close to the inner wall of the drilled hole and moreover the large number of temperature measuring holes differ in temperature measuring condition from each other thus deteriorating the measuring accuracy and degrading the control accuracy of the temperature control system with respect to all the coke ovens. PA1 (4) Since any damage and hence the occurrence of any cracks or the falling off of the joints at the bricks or mortar on the hole wall during the drilling causes the gas sealing of the coke oven to become insufficient and allow the waste gases to flow into the temperature measuring holes and corrode the thermocouples, the drilling apparatus and the drilling method must be such that no vibration or shock is applied to the brick. PA1 (5) Even if a hole is drilled smoothly, there is the danger of slight cracks or the breaking of joints occuring at the drilled hole wall and it is necessary to detect and mend such cracks or breaks and thereby completely prevent the leakage of the waste gases.
In the past, due to the absence of any other needs for making holes in the brick heated to an elevated temperature under such conditions as mentioned previously, the techniques of this kind have not been developed satisfactorily. In other words, the drilling and boring machines which have heretofore been used include various types of machines, such as, the drilling machine for drilling dynamite inserting holes in coal and other mines, the boring machine for the purpose of stratum analysis sampling in civil engineering works, the drilling machine for drilling concrete milk grouting holes in the base rock in the construction of a dam, the boring machine for oil well drilling purposes, etc., and these machines are such that .circle.1 the machines are used at the room temperature and therefore the frictional heat generated during the drilling operation is on the order of 200.degree. to 300.degree. C. .circle.2 Originally, there is no need to give much consideration to the occurrence of damages to the inner surface of the holes or the surrounding thereof. .circle.3 Considerable vibrations are caused. .circle.4 No precise drilling or boring and vertical accuracy are required.
On the other hand, the top brick of a coke oven is at an elevated temperature as mentioned previously. In other words, as for example, the temperature at the bottom of the flues of the combustion chamber reaches 1,150.degree. to 1,250.degree. C. and therefore the temperature of the oven top brick above the combustion chamber reaches about 1,000.degree. C. FIG. 1 shows the actual measured values in the "temperature distributions for the coke oven roof drilled hole portions" showing that the temperature at the drilled hole depth of 1,000 mm or the position of 1 m below the coke oven proper top surface is between 780.degree. and 820.degree. C. and the temperature at the position of 2 m below the top surface is between 890.degree. and 960.degree. C. (The thickness of the top brick at the time of the measurement was 2,450 mm).
Since a frictional heat is added by the drilling, the drilling bit is used at elevated temperatures of 1,200.degree. C. or over and therefore the conventional drilling machines for cold drilling purposes cannot be used from the standpoint of heat-resisting and wear-resisting properties.
Moreover, since the oventop brick is built by joining small bricks of about 230.times.115.times.145 together with mortar, if the boring drill speed, the rate of drilling, the bit shape, etc., are not carefully selected and if the occurrence of vibrations, shock or the like is not prevented completely, there is the danger of causing cracks at the mortar joints and this some times causes cracks in the brick or breaking off of the mortar thus causing the combustion gas to enter the drilled holes and thereby making it impossible to use the conventional boring and drilling machines due to such danger.
Moreover, assuming that the entire length of a boring drill is 3 m, that the diameter of each drilled hole is 62 mm and that a thermocouple having a diameter of 20 mm is vertically hang down and inserted into the hole, the near distance between the drilled hole wall and the thermocouple forward end will be 21 mm if the drilled hole is vertical completely, and the forward end (the temperature measuring portion) of the thermocouple will contact with the hole side wall if the drilled hole verticality involves an error of 1/100. Also, since the variation in near distance is great among a large number of temperature measuring holes and since the desired accuracy for the measured temperatures at the holes and the desired measuring accuracy among the holes cannot be expected, the drilled hole verticality must be 1/500 or less. It is practically impossible for the previously mentioned conventional drilling machines to effect the drilling operation with such accuracy of drilled hole verticality.